Method of recording and reproducing sound



March zl, 1939. c, 1c R 2,151,408

METHOD OF RECORDING AND REPRODUCING SOUND Filed July 15, 1936 2 Sheets-Sheet l fi z E925 Tim:

TiME

MarchZl, 1939. PJC RICCHIARDI 2,151,408

METHOD OF RECORDING AND REPRODUCING SOUND Filed July 15, 1936 2 Sheets-Sheet 2 Patented Mar. 21, 1939 PATENT OFFICE METHOD OF RECORDING AND REPRODUC- ING SOUND Pier Carlo Ricchiardi, Paris, France Application July 15, 1936, Serial No. 90,801

Claims.

In order to obtain a perfect reproduction of sounds recorded on a film, an accurate reproduction of the frequencies set into play does not sufiice. It is also necessary that, when record- 5 ing, the variations of volume should be in the same proportion as those due to an orchestra.

An object of the invention is to provide a method of producing a sound record on a film which comprises in conjunction with the record- 10 ing of the sound frequency modulation together with the inherently limited sound volume variations, another recording of the full sound volume variations.

Another object of the invention is to provide a method of producing a sound record on a single film which comprises, in conjunction with the recording of the uniform density and variable area type of the sound frequency modulation together with the inherently limited sound volume variations, another recording of the variable density type of the full sound variations, this latter record acting in addition to the sound volume variations registered by the first record for reproducing purposes, whereby a double volume control is obtained.

A further object of the invention is to provide a method for recording sounds on a film which comprises means for transforming sound intensity modulation together with the inherently limited sound variations into variations of position of a light ray so as to form a uniform density area sound track on said film, and means for varying the intensity of said ray iii-accordance with variations of sound volume.

5 A further object of the invention is to provide a method of producing, and/or playing off from, a film bearing two records, in such a manner that one of said records controls the amplification factor of the other record.

Furthermore, the background noise is due essentially to the grain of the film and it is proportional to the transparency of the sound band.

Consequently, the modulation (pianissimo) is the less intensive as the background noise is more accentuated.

In order to obtain a recording and a reproduction which are perfect from the point of View of the quality of the sounds, it is necessary to avoid not only any distortion in the frequencies at the present time, in which the sound is artificially reduced in the case of fortissimo. In other words, with the systems employed at the present time, the recording is effected within a range of variations of about 35 or 40 decibels, whereas the variations of volume of an average orchestra correspond to a range of more than decibels.

The object of the present invention is to provide a sound recording and reproducing system which obviates these drawbacks.

The essential feature of the present invention consists in simultaneously forming two records, one of the variable surface and uniform density type corresponding to modulations of the sound intensity and the other of the variable density type corresponding to variations of the sound volume.

Other features of the present invention will result from the following detailed description of some specific embodiments thereof.

Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example, and in which:

2 Fig. 1 is a plan view of a portion of a sound band recorded in the usual manner;

Fig. 2 is a plan view of a portion of a sound band recorded according to the principle of the present invention;

Fig. 3 is a diagram of the variations of intensity of this sound Wave;

Fig. 4 is a view of a portion of a sound band of the so-called triangular type recorded in the usual manner;

Fig. 5 is a view of a portion of a sound band of a similar type, recorded according to the principle of the present invention;

Fig. 6 is a diagram of the variations of intensity corresponding to this band;

Fig. 7 is a diagrammatical view of a recording apparatus according to the invention;

Fig. 8 is a diagram of the brilliance of the lamp working according to the principle of the present invention;

Fig. 9 is a diagram of a plant for reproduction of sound from sound bands according to the present invention.

An examination of Figs. 1 to 6 shows how the method according to the present invention is applied to photo-electrical records of the uniform density and variable width type. The sound band (Fig. 1) has an edge which is partly black, while the other edge is partly translucent or transparent. Modulation is represented by ridges l which vary with musical frequencies the energization of the reading cell in the usual manner. If now the sound band according to the present invention is examined (Fig. 2), it shows, on the one hand, frequency variations (modulation) supplied by ridges l and on the other hand volume variations due not only to variations of Width of pointed parts I but also to variations of transparency resulting from the presence of zones Y of variable transparency. These last mentioned variations control merely the sound volume and. they are combined to the variations concerning modulation.

The variations of intensity are so slow as compared with the variations of frequency that these respective variations cannot interfere mutually in View of the great difference of the frequencies set into play. For practical purposes, the variations of intensity may be considered as variations of intensity of direct current since the rate of one variation per second is hardly obtained, whereas the variations of frequency corresponding to modulation will always be alternating current variations ranging from 30 to 10,000 periods per second.

The diagram of Fig. 3 indicates the respective variations of intensity as a function of time resulting from the variations of transparency of zones Y formed on the band (Fig. 2).

Fig. 4 shows a uniform density record band. of the so-called triangular type, such as it is recorded in the usual manner.

Fig. 5 shows a band of the same kind recorded according to the principle of the present invention, whereas Fig. 6 is a diagram analogous to that of Fig. 3.

To sum up, the method of recording sounds according to the present invention is intended to increase the field of the variations of intensity so as to reproduce the sounds with the original colour thereof. This method consists in combining the uniform intensity recording system and the variable density recording system.

The characteristic feature of the process ac cording to the invention lies essentially in the fact that one kind of record controls exclusively modulation, whilethe other type of record controls exclusively the sound volume.

The method above described can be carried out by means of the device shown in a diagrammatic manner in Fig. '7 of the drawings.

The recording being effected with the uniform density method, the current leaving microphone E is amplified and flows through the last lamp D and the primary T of the output transformer. The secondary C is connected to the os'cillograph B. The light ray issuing from lamp L and passing through the optical device A strikes the mirror or oscillograph B. This light ray is modulated and passes through the optical device F, the slot G, the optical device H, and acts upon film M according to the usual effect illustrated by Fig. 1. But, at the same time as this first recording is effected, a second recording, adapted to control the sound volume is also obtained. For this purpose, the output transformer T is provided with another secondary N. In the circuit of this secondary there is inserted a battery P intended to feed current to the illuminating lamp L.

This lamp L is brought to a point of brilliance lower than its maximum value in such manner that, when there is a fortissimo of the orchestra, this lamp can be given its maximum brilliance. In the circuit of the second secondary N, there Due to the permanent current produced by 0 battery P, the level VP corresponding to the minimum of illumination, that is to say to a pianissimo of the orchestra or more accurately to the absence of modulation, is obtained. But as the volume of the sounds emitted by the orchestra. increases, a supplementary unidirectional current flows through the circuit and increases the illumination of lamp L. Thus the level V0 corresponding to average register is obtained, same as the upper level corresponding to fortissimo.

- The brilliancy of the lamp therefore varies in accordance with the variations of volume of the sounds, whereas the frequencies have no effect because a unidirectional current is caused to flow and the filament of the lamp opposes any rapid variation owing to its thermal inertia, which acts in a manner analogous to a fiy-wheel' The light rays that strike the mirror of oscillograph B, instead of having a fixed luminous intensity, have, on the contrary, an intensity that varies according to the sound volume between levels VM and VP (Fig. 8). Therefore, the sound record is formed on the film as illustrated by Figs. 2 and 5.

Finally, I therefore obtain on the film a sound record which results upon both sound volume variations due to normal recording and also.

variations due to the difference of illumination of the energizing lamp.

The system illustrated by the drawings is described merely by way of example. obvious that, instead of varying the illumination It is quite of the lamp I'might employ any other system acting upon the density'of the light ray or upon the optical device, or upon the oscillograph device. I might dispose across the path of travel of the light ray a Kerr cell, for instance energized through a circuit: analogous to the energizing circuit of lamp L. I might also interpose a filter across said circuit withoutchanging anything to the characteristics of the method according to the present invention, which consist essentially in applying two recording systems to the film, one of these systems serving to record modulations and the other to simultaneously record variations of the sound volume.

In the reproduction of a band according to Figures 2 and 5 one will have, therefore, quick variations with a musical frequency to 10,000 hertz) due to the record of the reading of the modulation and its normal variations of the depth of modulation, as well as the slow variations due to the transparency of the sound track and resulting from the sound volume record.

Since the volume variations which are inscribed with the modulation are only the diiference of magnitude of each ridge or crest with respect to the following crest they result in voltage variations on the grid of the amplifier tube and with a frequency which is equal to the modulation frequency.

Asa consequence, in the reproduction, as the modulation varies in frequency (between 20 and 10,000 cycles), volume variations will attack directly the main grid of the amplifier tube. Figure 9 shows, by way of example, the diagram of a system adapted for the reproduction of this film. According to this diagram, both bands recorded on the film are read at the same time through the photo-electric cell D The outlet conductor of this cell is connected to the main grid G of the amplifier tube D through a condenser C and in front of this condenser a filter L is connected to the said conductor. Since the impulses of the modulated current have a frequency which is higher than the frequency of the filter L they pass through the condenser C impart a modulated voltage to the terminals of the resistance R and pass to the main grid G of the tube D The variations of the sound volume record result in slow variations (with respect to the modulation frequency) of the transparency of the sound band, or in slow variations of the direct current which flows through thecircuit of the photo-electric cell D Consequently, the latter variations cannot pass through the condenser C (Fig. 9) and therefore they cannot influence the main grid G of the amplifier tube D, but they will find a passage almost without any resistance through the whole filter assembly L Thus, the two volume controls cannot, possibly, influence one another.

Supposing now that the reading is effected on a more translucid zone, the cell D receives a more powerful lighting effect; one has, therefore, a greater passage of direct current in the circuit of the cell independently of the normal variations of the modulated current. This direct current causes a greater voltage fall through the resistance R and with respect to the mass the positive terminal of said resistance will be more positive than in the case when a gray zone of the film is considered, where the direct current which flows through the circuit of the cell is then smaller. But the resistance R is nothing other than the polarization resistance of an auxiliary or cathodic grid 9 controlling the factor of amplification of the tube D Since this resistance is more positive, it results therefrom that the tube amplifies in a greater degree the voltage oscillations corresponding to the modulated current and which are applied to the main grid.

For obtaining the same result it is, moreover, possible to leave opaque the zone proper to the modulation in Figures 2 and 5 and to vary the transparency of the zone which is translucid, as it is known, by the usual methods. This zone will then have a transparency which is proportional to the sound volume.

It is possible that the mean sound level which is supplied by the modulated track is slightly lower than the level obtained with a normal track, since the contrast between the modulation and the carrier is less accentuated, but experience shows that this slight fall of power is largely compensated by the action of the sound volume record. It is also obvious that a suitable use of the characteristics of the amplifier tube D permits the obtaining of a great variation in the amplification factor and that these variations of the direct current which flows through the circuit of the photo-electric cell can be amplified or not amplified, according to the importance of the amplification factor which it is desired to obtain.

Moreover it is obvious that the same arrangement of photo-electric reader cells with its filtering devices is applicable to and covers the reproduction of the records with multiple bands, one of which, at least, is assigned to the modulation and the others to the expansion controls and, essentially, when the width of all these bands is equal to the width of a normal band so that they may be read simultaneously by a single revealer.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiments of the present invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and" form of the parts without departing from the principle of the present invention as comprehended within the scope of the appended claims. What I claim is:

1. A method for reproducing and amplifying sound from a film bearing a plurality of sound records, one of which records comprises a sound frequency modulation together with the corresponding normal sound volume variations, and another of which records comprises additional sound volume having a lower frequency than that of said sound frequency modulation record, said method comprising simultaneously picking up the impulses of each record with a common means, filtering said impulses to separate the modulation record impulses from the lower frequency impulses of the additional volume record and passing the separated impulses through amplifying means, and employing the impulses of the additional volume record passing through the filtering means to control the amplification factor of said amplifying means.

2. A method for reproducing and amplifying sound from a plurality of sound records, one of which records comprises a sound frequency modulation together with the corresponding normal sound volume variations, and another of which records comprises additional sound volume, said method comprising simultaneously picking up the impulses of each record, separating the modulation record impulses from the impulses of the additional volume record and passing the separated impulses through amplifying means, and employing the impulses of the additional volume record to control the ampli fication factor of said amplifying means.

3. A method of producing a sound record on a single film and reproducing and amplifying sound from said film comprising, in conjunction with the recording of the sound frequency modulation together with the inherently limited sound volume variations, another recording of the full sound volume variations and reproducing said records by simultaneously picking up the impulses of each record, separating the sound frequency modulation record impulses from the impulses of the additional volume record and passing the separated impulses through amplifying means, and employing the impulses of the additional volume record to control the amplification factor of said amplifying means.

4. An apparatus for reproducing and amplifying sound from a record system including at least two sound records, one of which comprises a sound frequency modulation together with the corresponding normal sound volume variations, and the other comprises an additional sound volume record impulses, and means, inserted between said auxiliary grid and said receiving circuit, in shunt with said first mentioned transmission means, for transmitting the lower Irequency volume record impulses to said auxiliary grid, while stopping transmission of'the modulation record impulses to said auxiliary grid.

5. An amplifying apparatus for reproducing sound from a film bearing at'least two sound records, one of which comprises a sound frequency modulation together with the corresponding normal sound volume variations, and the other comprises an'additional sound volume variation of lower frequency than that of said sound frequency modulation record, which comprises, in combination, an amplifying system including a multi-electrode electron tube having a main grid and at least one auxiliary grid for controlling the amplification factor of said tube, a receiving circuit, a photo-electric cell in said 'circuit, operative by both of said film records, for controlling the current flowing through said circuit, transmission means, including at least one condenser, interposed between said receiving circuit and said main grid, forimpressing on said grid the modulation record impulses, while stopping transmission of the lower frequency additional volume record impulses to said main grid, and filtering means, inserted between said auxiliary grid and said receiving circuit, in'shun't with said first mentioned transmission means, for transmitting the lower frequency volume record impulses to said auxiliary grid, while stopping transmission of the modulation record impulses thereto.

PIER CARLO RICC'HIARDI. 

